It is known to use wireless power transmission in situations where physical wiring or cabling between a power source and a power consumption point is difficult, if not impossible, to implement. Electromechanical devices conventionally employ inductive elements for power transmission e.g. between rotating or otherwise separated components. Inductive power transmission is also used for recharging low-power batteries, for example. In inductive power transmission, the power source and the power consumption or recharging point must be located close to each other, and it is often necessary to isolate them galvanically from the environment, because the electromagnetic radiation caused by induction may interfere with the operation of adjacent devices.
Solutions are also known wherein power transmission is carried out as radio frequency transmission from a transmitter to one or more receivers, such as radio-frequency identification and key cards. Such a solution is only suitable for power transmission of a very low level, because it is difficult to direct the total power to be used for the transmission at specific receiving antennas, and in practice transmission losses are extremely large. In addition, the efficiency of radio frequency power transmission degrades rapidly as a function of distance.
A possibility to carry out wireless power transmission is to use a light source as the power transmitter, the transmitted light then being received by a photo-detector and converted into electric current. A light source is easier to direct towards a receiver, and this enables a better efficiency than that achieved e.g. in radio frequency power transmission to be achieved. Publications EP 734 110 and U.S. Pat. No. 4,078,747, for example, describe solutions wherein high power lasers are used for wireless transmission of high currents in the power supply of electric trains and, similarly, for transferring solar energy generated in space.
A problem with the above-described solutions is that they are not suitable for efficient wireless power transmission in environments occupied by people since the intensity of the laser to be used is substantially life-threatening. Even if significantly reduced, the power levels required for a sufficiently good efficiency would be so high that the laser would at least severely damage vision in case of ocular exposure. The aforementioned safety problems further present the disadvantage that although optical data transmission is known per se, such transmission is difficult to implement wirelessly in a safe manner; therefore, an optical fibre is typically used for optical data transmission.